/Engine/Plugins/Online/OnlineSubsystem/Source/Public/OnlineSubsystem.h
Common implementation for finding a player in a session
true if unique id found in session, false otherwise
bool IsPlayerInSessionImpl ( class [IOnlineSession](API\Plugins\OnlineSubsystem\Interfaces\IOnlineSession) * SessionInt, [FName](API\Runtime\Core\UObject\FName) SessionName, const [FUniqueNetId](API\Runtime\CoreOnline\Online\FUniqueNetId) & UniqueId )